The most common and most likely answer to this crossword clue is the 3 letter word LED
I've seen this crossword clue in The Daily Telegraph
L
E
D
More clues leading to the result LED
Buddy explains!
The straight part
We know that "Was first/replacement for tungsten lamp" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case was first/replacement for tungsten lamp = led.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LED mean?
LED verb- (heading) To guide or conduct.
- To guide or conduct, as by accompanying, going before, showing, influencing, directing with authority, etc.; to have precedence or preeminence; to be first or chief; — used in most of the senses of the transitive verb.
- (heading) To begin, to be ahead.
- To draw or direct by influence, whether good or bad; to prevail on; to induce; to entice; to allure
- To tend or reach in a certain direction, or to a certain place.
- To produce (with to).
- (transitive) To live or experience (a particular way of life).
- Under somebody's control or leadership.